Chlorinated, alumina-based, bimetallic catalyst and its use in the isomerization of C4 -C6 paraffins

ABSTRACT

A catalyst is provided based on chlorinated eta alumina incorporating platinum and germanium and tin, as well as chlorine. This catalyst can be used in a process for the isomerization of a charge rich in normal C 4  -C 6  -paraffins, without hydrogen recycling.

The present invention relates to a novel bimetallic catalyst based onchlorinated alumina and its use in a process for the isomerization ofnormal C₄ -C₆ paraffins not requiring hydrogen recycling.

BACKGROUND OF THE INVENTION

As a result of the elimination, mainly for ecological reasons, of leadalkyls in gasoline, the isomerization of normal paraffins having 4 to 6carbon atoms is at present of considerable importance in the petroleumindustry.

The isomerization of n-butane makes it possible to produce isobutane forthe aliphatic alkylation of olefins and the synthesis of MTBE (methyltert. butyl ether), respectively making it possible to produce analkylate having a high octane number which can be incorporated into thegasoline pool and supply MTBE used as an octane additive.

The isomerization of normal C₅ -C₆ paraffins makes it possible totransform these low octane number paraffins into high octane numberisoparaffins.

Three different types of catalysts are conventionally used for carryingout this isomerization reaction:

Friedel-Crafts catalysts, such as aluminium chloride, which are used atlow temperatures (approximately 20° to 130° C.);

catalysts based on metals of group VIII on halogenated alumina, whichare used at medium temperatures (approximately 150° C.);

zeolitic catalysts incorporating a metal of group VIII deposited on azeolite and which are used at high temperatures (250° C. and higher);

these catalysts leading to reduced octane number improvements, but havethe advantage of being easier to obtain and are more resistant topoisons, but as a result of their low acidity, they cannot be used forn-butane isomerization.

Numerous patents deal with monometallic catalysts based on platinumdeposited on a halogenated alumina, said catalysts being used in theisomerization of normal paraffins, in which the molarhydrogen/hydrocarbon (H₂ /HC) ratios are relatively high, in order toprevent deactivation by coking linked with secondary reactions or thetemporary presence of sulphur, cf. e.g. U.S. Pat. No. 2,906,798, inwhich H₂ /HC is higher than 0.17, U.S. Pat. No. 2,993,398 and U.S. Pat.No. 3,791,960, in which H₂ /HC is respectively between 0.2 and 10 andbetween 0.1 and 15, as well as U.S. Pat. No. 4,113,789 and U.S. Pat. No.4,149,993, in which H₂ /HC is approximately 0.2.

More recently, U.S. Pat. No. 4,804,803 claims the use of a monometalliccatalyst having a greater resistance to deactivation, more particularlyin the presence of sulphur, in a process for the isomerization of normalparaffins and without hydrogen recycling, using H₂ /HC molar ratios inthe effluent of below 0.05. These low ratios minimize the costs of theprocess, because they require no hydrogen separation apparatus orcompressor for the recycling thereof.

SUMMARY OF THE INVENTION

The object of the present invention is the use of a novel bimetalliccatalyst (incorporating at least two metals) based on chlorinatedalumina and having, apart from a high selectivity and activity, aconsiderably improved coking resistance and therefore stability,permitting the use thereof in a process for the isomerization of normalC₄ -C₆ paraffins not requiring hydrogen recycling and with a longercycle time.

The catalyst according to the invention is based on chlorinated etaalumina containing 0.01 to 0.4 and preferably 0.015 to 0.025% by weightof a metal from group IV A of the periodic classification of elements,such as tin or germanium and preferably tin, 0.05 to 0.6 and preferably0.15 to 0.4% by weight of a metal of group VIII of the periodicclassification of elements, preferably platinum, and 1 to 12 andpreferably 4 to 10% by weight of chlorine.

The preferred alumina is eta alumina, which leads to a regeneratablecatalyst particularly due to its greater chlorination facilityassociated with its high specific surface of approximately 400 m² /g (R.G. MCCLUNG, J. S. SOPKO et al, 1990, NPRA, Annual Meeting San Antonio).

The catalyst according to the invention can be prepared by differentalumina impregnation methods, but the invention is not limited to aparticular method. The impregnation operation, e.g., consists ofcontacting the alumina and an aqueous or organic solution of a compoundof the chosen metal or metals, the volume of said solution being inexcess or equal to the alumina retention volume.

The metal of group VIII, preferably platinum, is thus generallydeposited on the alumina by anion exchange with a hexachloroplatinicacid solution. It is also possible to use other compounds of said acid,such as ammonium chloroplatinate, bromoplatinic acid or platinumchloride.

The metal of group IV A, generally tin or germanium, can be deposited onthe alumina already preimpregnated by the metal of group VIII andoptionally calcined and/or reduced, in an aqueous or hydrocarbonsolution. This metal can be introduced by means of compounds such aschlorides, nitrates, sulphates, acetates, amino complexes of tin orgermanium in aqueous solution and germanium or tin metallic aryl oralkyl compounds such as tetrabutyl tin, tetremethyl tin, diphenyl tin,tetrapropyl germanium and diphenyl germanium in hydrocarbon solution.

Once the metals are fixed to the alumina, the catalyst advantageouslyundergoes an activation treatment under hydrogen and at elevatedtemperature, e.g., at between approximately 300° and 500° C., in orderto obtain an active metal phase. The procedure of this treatment underhydrogen e.g., consists of slowly raising the temperature under ahydrogen flow to the maximum reduction temperature, which is generallybetween approximately 300° and 500° C. and is preferably betweenapproximately 340° and 470° C., followed by the maintaining of saidtemperature for 1 to 6 hours and preferably 1.5 to 4.5 hours.

The chlorination of the alumina takes place outside or directly in theisomerization unit using any known chlorinating agent, such as e.g.carbon tetrachloride, dichloroethane or dichloropropane, e.g. at atemperature between approximately 200° and 350° C.

The catalyst according to the invention is advantageously used in aprocess for isomerizing a charge rich in normal C₄ -C₆ paraffins withouthydrogen recycling, which constitutes another object of the invention.

The term "rich" means that the charge contains at least 50% andpreferably at least 80% normal C₄ -C₆ paraffins. The preferred chargesare essentially constituted by normal C₄ -C₆ paraffins. These chargesare, e.g., n-butane and/or C₅ -C₆ fractions, e.g., resulting from directdistillation or catalytic reforming.

The charge is advantageously carefully dried and preferably containsless than 0.2 ppm water and less than 0.5 ppm sulphur and nitrogen, dueto the sensitivity to water and impurities of platinum catalysts basedon chlorinated alumina. In order to achieve such contents, it ispossible to use known, specific adsorbents.

In the isomerization process according to the invention a mixtureconstituted by the charge and hydrogen is contacted in a reaction zonewith at least one catalyst according to the invention and describedhereinbefore under isomerization conditions.

The isomerization conditions in the reaction zone and in particular thetemperature are dependent on the charge to be treated. As isoparaffinsare favored at low temperatures, from a thermodynamic standpoint, theperformance characteristics of the catalyst will improve when working atlower temperatures. The temperature in the reaction zone is normallybetween 40° and 230° C. In cases where the charge essentially containsn-butane or essentially normal C₄ -C₆ paraffins, the temperature isnormally between 130° and 230° C. and preferably between 140° and 220°C. In the case where the charge essentially contains normal C₅ -C₆paraffins, the isomerization is easier to carry out and the temperatureis then usually between 40° and 190° C. and preferably between 70° and170° C. The pressure in the reaction zone can vary within a relativelywide range and is normally between 10 and 50 bars, preferably between 15and 35 bars. The charge flow rate in the reaction zone can also varywithin a relatively wide range, the space velocity normally beingbetween 0.4 and 15 h⁻¹, preferably between 1 and 5 h⁻¹.

A chlorine concentration in the reaction zone is maintained at between20 and 1000 ppm, preferably between 50 and 300 ppm. Thus, in order tomaintain the chlorine content of the catalyst and therefore its acidity,it is necessary to continuously inject into the reaction zone, e.g., bymeans of the charge, a chlorine promoter, such as carbon tetrachlorideor hydrogen chloride.

The hydrogen quantity mixed with the charge is such that the effluentdrawn off from the reaction zone has a molar hydrogen/hydrocarbon (H₂/HC) ratio below 0.05.

The molar hydrogen/hydrocarbon (H₂ /HC) ratio of the charge is then verylow and generally below 0.1, which is made possible by the improvedcoking resistance of the catalyst used.

The effluent from the reaction zone is separated into a mixture of C₄-C₆ hydrocarbons incorporating the C₄ -C₆ isoparaffins obtained andpossibly normal C₄ -C₆ paraffins not yet converted and a gaseous mixturecontaining hydrogen and light hydrocarbons, said gaseous mixture beingeliminated from the process without hydrogen recycling. The cost of theprocess is very low, because it does not require a hydrogen separatingapparatus or a compressor for the recycling thereof. The unconvertednormal C₄ -C₆ paraffins contained in the effluent from the reaction zoneare generally recycled, at least in part, to the said reaction zone.

The reaction zone can optionally have at least two reactors in series inwhich the temperatures are different, the temperature in the secondreactor generally being below that in the first reactor.

The following examples illustrate the invention without limiting thescope.

The catalytic performance characteristics are expressed by the ratios##EQU1##in which x is 4, 5 or 6, iC_(x) representing the isoparaffinquantity with x carbon atoms in the effluent and (i+n)C_(x) representsthe isoparaffin and normal paraffin quantity with x carbon atoms in theeffluent and the approaches to equilibrium on the different isomersdefined hereinafter: ##EQU2##with i_(x) =isoparaffin with x carbon atoms(x=4, 5 or 6).

EXAMPLE 1: CATALYST A (ACCORDING TO THE INVENTION)

Following the prior calcination of the eta alumina, deposition takesplace thereon of 0.3% platinum by anion exchange with hexachloroplatinicacid inthe presence of HCl as the competing agent. The thus preparedsolid is calcined and then reduced at 350° C. 200 ppm of tin are thendeposited, while refluxing for 5 hours under an inert gas in a heptanesolution containing tetrabutyl tin the previously prepared solid. Thesolution is then eliminated and replaced by a fresh heptane solution.The solid is washed for 2 hours under reflux in said solution. Thesolution isthen eliminated and the solid is dried in a rotaryevaporator. The thus prepared solid is fed into a reactor and thendirectly reduced within the latter at 450° C. for 4 hours. This isfollowed by chlorination at 280° C. by the injection of CCl₄ at a rateof 0.3 cm³ of CCl₄ per gram of catalyst. The chlorine content on thefinal catalystis then approximately 6% by weight.

EXAMPLE 2: CATALYST B (NOT ACCORDING TO THE INVENTION)

Catalyst B differs from catalyst A prepared in example 1 solely in thatit does not contain tin. The platinum deposition, heat treatment andchlorination stages are identical to those described in example 1.

EXAMPLE 3: ISOMERIZATION TEST FOR NORMAL C--C PARAFFINS

The previously prepared catalysts A and B are each tested in theisomerization of a charge formed from approximately 60% normal C₅paraffins and 40% normal C₆ paraffins, said charge containing 100 ppmofCCl₄, expressed as chlorine weight, for maintaining the chlorine contentof the catalyst used.

The operating conditions are as follows:

Temperature: 150° C.

Pressure: 20 bars

Space velocity: 2 h⁻¹

H₂ /HC (in the effluent): 0.05.

The performance characteristics after 24 and 2160 hours of operation aregiven in table 1, there being essentially no deactivation of catalyst A,but a significant deactivation of catalyst B.

EXAMPLE 4: ISOMERIZATION TEST FOR N-BUTANE

Previously prepared catalysts A and B are each tested in theisomerization of a n-butane charge containing 100 ppm of CCl₄, expressedas chlorine weight.

The operating conditions are as follows:

Temperature: 200° C.

Pressure: 20 bars

Space velocity: 2 h⁻¹

H₂ /HC (in the effluent): 0.05.

The performance characteristics obtained after 24 and 2160 hours ofoperation are given in table 2, there being no deactivation of catalystA,but a significant deactivation of catalyst B.

EXAMPLE 4

The previously prepared catalyst B is tested under the same conditionsas those of example 3, except that the H₂ /HC ratio (in the effluent)ishigher, being namely 1.

The performance characteristics obtained after 24 and 2160 hours ofoperation are given in table 3, there being no deactivation of catalystB.

                  TABLE 1                                                         ______________________________________                                                     Catalysts                                                                     A          B                                                                  After After    After   After                                                  24 h. 2160 h.  24 h.   2160 h.                                   ______________________________________                                        iC.sub.5 /(i + n)C.sub.5                                                                     0.762   0.760    0.762 0.70                                    iC.sub.6 (i + n)C.sub.6                                                                      0.895   0.890    0.895 0.78                                    AEQ i.sub.5 (%)                                                                              95.3    95.0     95.3  87.5                                    AEQ 22 DMC.sub.4 (%)                                                                         87.8    87.0     87.8  75.6                                    Cracking (% by weight)                                                                       3.05    2.0      3.2   2.5                                     (secondary reaction)                                                          ______________________________________                                        with 22 DMC.sub.4 = 2,2dimethyl butane)                                   

                  TABLE 2                                                         ______________________________________                                                    Catalysts                                                                     A               B                                                             After After     After   After                                                 24 h. 2160 h.   24 h.   2160 h.                                   ______________________________________                                        iC.sub.4 (i + n)C.sub.4                                                                     0.5     0.5       0.5   0.4                                     AEQi.sub.4 (%)                                                                              100     100       100   80                                      Cracking (% by                                                                              2.2     2.0       2.5   2.2                                     weight (secondary                                                             reaction)                                                                     ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                       Catalyst B                                                                    After 24 h.                                                                           After 2160 h.                                          ______________________________________                                        iC.sub.5 /(i + n)C.sub.5                                                                       0.762     0.760                                              iC.sub.6 /(i + n)C.sub.6                                                                       0.895     0.890                                              AEQi.sub.5 (%)   95.3      95.0                                               AEQ 22 DMC.sub.4 (%)                                                                           87.8      87.0                                               Cracking (% by weight)                                                                         3.2       3.0                                                (secondary reaction)                                                          ______________________________________                                    

We claim:
 1. A catalyst composition consisting essentially of etaalumina; 0.01% to 0.4% by weight of a group IV A metal wherein saidgroup IV A metal is germanium or tin; 0.05% to 0.6% by weight ofplatinum; and 1% to 12% by weight of chlorine.
 2. A catalyst accordingto claim 1, wherein the weight content of germanium or tin is0.015%-0.25%, the weight content of platinum is 0.15%-0.4% and theweight content of chlorine is 4%-10%.
 3. A catalyst compositionaccording to claim 1 wherein said metal of group IV A is germanium.
 4. Acatalyst composition according to claim 1 wherein said metal of group IVA is tin.
 5. A process for the isomerization of a charge rich in normalC₄ -C₆ -paraffins without hydrogen recycling, comprising:contacting amixture of said charge and hydrogen in a reaction zone with at least onecatalyst according to claim 1 under isomerization conditions;maintaining a chlorine concentration in said reaction zone at 20ppm-1000 ppm; and separating effluent from said reaction zone into C₄-C₆ -isoparaffins and a gaseous mixture containing hydrogen, saidgaseous mixture being eliminated from said process without recycling thehydrogen to said reaction zone, wherein the hydrogen quantity mixed withsaid charge is such that the effluent from said reaction zone has ahydrogen/hydrocarbon molar ratio of below 0.05.
 6. A process accordingto claim 5, wherein said hydrogen/hydrocarbon molar ratio of the chargeis below 0.1.
 7. A process according to claim 5, wherein in saidreaction zone, the temperature is 40° C.-230° C., the pressure is 10bars-50 bars and the space velocity is 0.4 h⁻¹ -15 h⁻¹.
 8. A processaccording to claim 5 wherein the unconverted normal C₄ -C₆ paraffinscontained in said effluent from said reaction zone are at least partlyrecycled to said reaction zone.
 9. A process according to claim 5wherein said reaction zone has at least two reactors in series.
 10. Acatalyst composition according to claim 2, wherein said metal of groupIV A is germanium.
 11. A catalyst composition according to claim 2,wherein said metal of group IV A is tin.
 12. A catalyst compositionaccording to claim 11, produced by a process comprising:(a) calciningeta alumina, (b) depositing platinum on said eta alumina by anionexchange with hexachloroplatinic acid in the presence of HCl, (c)calcining the resultant composition and reducing the resultant calcinedcomposition, (d) refluxing the resultant reduced composition in asolution containing a tin compound and drying the resultanttin-impregnated composition, (e) reducing the resultant dried catalystcomposition, and (f) chlorinating the resultant reduced composition fromthe prior step.
 13. A catalyst composition according to claim 12,wherein the resultant calcined composition is reduced at 350° C. in step(c) and the dried catalyst is reduced at 450° C. in step (e) and is thenchlorinated at 280° C. by the injection of carbon tetrachloride in step(f).
 14. A catalyst composition according to claim 1, wherein thechlorine weight content of said catalyst is 4%-10%.
 15. A catalystcomposition consisting of eta alumina; 0.01%-0.4% by weight of germaniumor tin; 0.05%-0.6% by weight of platinum; and 1%-12% by weight chlorine.16. A catalyst composition according to claim 15, wherein the chlorineweight content of said catalyst is 4%-10%.
 17. A catalyst compositionaccording to claim 4, produced by a process comprising:(a) calcining etaalumina, (b) depositing platinum on said eta alumina by anion exchangewith hexachloroplatinic acid in the presence of HCl, (c) calcining theresultant composition and reducing the resultant calcined composition,(d) refluxing the resultant reduced composition in a solution containinga germanium compound and drying the resultant germanium-impregnatedcomposition, (e) reducing the resultant dried catalyst composition, and(f) chlorinating the resultant reduced composition from the prior step.18. A catalyst composition according to claim 17, wherein said germaniumcompound is a chloride, nitrate, sulfate, acetate, amino complex, alkylor aryl compound.
 19. A catalyst composition according to claim 12,wherein said tin compound is a chloride, nitrate, sulfate, acetate,amino complex, alkyl or aryl compound.
 20. A catalyst compositionaccording to claim 19, wherein said tin compound is tetrabutyl tin,tetramethyl tin or diphenyl tin.
 21. A catalyst composition according toclaim 20, wherein said tin compound is tetrabutyl tin.
 22. A catalystcomposition according to claim 18, wherein said germanium compound istetrapropyl germanium or diphenyl germanium.
 23. A catalyst compositioncomprising eta alumina; 0.01% to 0.4% by weight of germanium or tin;0.05% to 0.6% by weight of a single metal of group VIII of the periodicclassification of elements wherein said metal is platinum; and 1% to 12%by weight of chlorine.